Optimize conversation restoration startup and reduce redundant sidebar recomputation

[devin-ai-integration]

Summary

Eliminates a 2s+ main-thread hang during startup caused by the conversation restoration flow executing redundant activations, heavyweight property-observer side effects, and unnecessary SwiftUI animation computations synchronously. Also reduces ongoing sidebar recomputation cost by caching derived properties and using copy-modify-writeback for struct mutations.

Why

During startup, handleConversationListResponse restores ~50 conversations from the daemon. The previous implementation had several compounding costs:

• Double activation: activateConversation(firstVisible.id) triggered a full side-effect chain (VM creation, daemon HTTP call, Combine subscriptions), then restoreLastActiveConversation() could activate a different conversation — running the entire chain again.
• Heavyweight didSet: activeConversationId.didSet ran ~50 lines of synchronous side effects. Per Apple's Observation framework guidance, property observers should perform lightweight bookkeeping; side effects belong in explicit methods.
• Animation overhead: Bulk conversations array assignment triggered SwiftUI diffing and animation interpolation for every row. Apple's Transaction API allows suppressing this via disablesAnimations.
• Redundant computed properties: groupedConversations, visibleConversations, etc. were computed on every view body access. Multiple views reading the same property within a single layout pass each re-ran O(N log N) sort + O(N) filter independently. Apple recommends pre-computing expensive derived values outside the view body.

Changes

1. Eliminate double activation (ConversationRestorer): Activation target (saved last-active → first visible → new) computed once and activated once.

2. Decouple side effects from activeConversationId didSet (ConversationSelectionStore): didSet now does only UserDefaults persistence and stale-anchor clearing. Heavy work (VM creation, daemon notification, observation wiring) moves to explicit performActivation(for:) / performDeactivation(). Setter is private(set) — all callers go through these methods or the activateConversation() facade. performActivation(for:) short-circuits when the target is already active.

3. Suppress animations during bulk restoration (ConversationRestorer): Both groups and conversations assignments wrapped in withTransaction { disablesAnimations = true } per Apple's Transaction API.

4. Cache derived sidebar properties (ConversationListStore): groupedConversations, visibleConversations, sortedGroups, unseenVisibleConversationCount, archivedConversations converted to stored private(set) properties, recomputed once per conversations/groups mutation via didSet. Early-returns when conversations is empty.

5. Copy-modify-writeback for multi-field struct mutations (ConversationListStore, ConversationRestorer, ConversationManager): With change ci: add web and platform CI/PR workflows #4, each conversations[index].field = value triggers didSet → recomputeDerivedProperties() (O(N log N)). All multi-mutation paths now copy the struct locally and write back once:

   • Bulk loops (markAllConversationsSeen, restoreUnseen): snapshot pattern — N mutations → 1 writeback
   • Single-element multi-field (mergeAssistantAttention, pinConversation, unpinConversation, moveConversationToGroup, rollbackUnreadMutationIfNeeded, handleAssistantMessageArrival, handleNotificationIntentForExistingConversation): copy-modify-writeback → 1 didSet each
   • ConversationRestorer existing-conversation merge: non-attention fields → 1 writeback, then mergeAssistantAttention for pendingAttentionOverrides reconciliation → 1 more. Total: 2, down from 4.

6. Fix archiveConversation fallback selection (ConversationManager): visibleAfter/visibleBefore now exclude .private conversations, matching visibleConversations semantics.

7. Fix closeConversation stale selection (ConversationManager): Added performDeactivation() fallback when no next conversation exists.

Benefits

• Speed: Eliminates redundant activation cycle and O(N log N) recomputation on every struct-field mutation during hot paths. Animation suppression avoids SwiftUI diffing/interpolation for ~50 rows at startup.
• Maintainability: activeConversationId setter is private(set) with lightweight didSet — side effects are explicit and discoverable via performActivation/performDeactivation. Cached derived properties make the write-triggers explicit.
• Correctness: Archive fallback no longer selects private conversations. Close fallback no longer leaves stale selection.

Safety

• All existing activeConversationId = ... call sites migrated to performActivation(for:) / performDeactivation() (verified via grep). The private(set) access control will surface any missed callers as compile errors.
• Copy-modify-writeback preserves identical mutation semantics — same fields set to the same values, just batched into a single array writeback.
• withTransaction { disablesAnimations } only suppresses animation interpolation; it does not skip view updates. Views still reflect the new state.
• Remaining single-field mutations (title rename, resolveConversationId, backfillConversationId, unarchiveConversation) trigger exactly one recompute each and are unchanged.

References

• Managing model data in your app — Small, focused model objects with lightweight property observers
• WWDC23: Discover Observation in SwiftUI — Property-level tracking, observation best practices
• Understanding and improving SwiftUI performance — Pre-compute expensive values outside view bodies
• Transaction — Suppressing animations during programmatic updates
• WWDC21: Demystify SwiftUI — View identity, dependency management, avoiding unnecessary invalidation

Review & Testing Checklist for Human

• Build locally in Xcode — CI macOS checks are skipping. The private(set) change on activeConversationId will surface any missed callers as compile errors. This is the most important verification step.
• performActivation(for:) short-circuit guard — Verify no flow depends on re-activation when the conversation is already active (e.g., after VM eviction while a conversation remains selected). The guard conversationId != activeConversationId skips VM creation, daemon notification, and observation wiring.
• Startup with ~50 conversations — Launch the app, verify correct conversation activates (last-active if saved, otherwise first visible), sidebar populates without animation artifacts.
• Conversation switching / close / archive — Exercise switching, closing the last conversation, archiving adjacent to private conversations, draft mode entry/exit.
• Mark-all-seen → undo → mark-unread — Snapshot-writeback batches mutations atomically. Verify the full cycle works correctly.
• Pin / unpin / move-to-group — These use copy-modify-writeback. Verify pin, unpin (including heuristic group restoration for legacy pins), and drag-to-group.

Notes

• import SwiftUI added to ConversationRestorer.swift (model-layer file) for Transaction/withTransaction. This is the Apple-recommended API but is a layering consideration.
• lastActiveConversationIdString added to MockConversationRestorerDelegate to satisfy the updated ConversationRestorerDelegate protocol.
• ConversationManager.activeConversationId facade is now read-only. All activation routes through activateConversation() / enterDraftMode().
• Last-active restoration uses local UUIDs which are regenerated on cold restart, so activationTarget only helps on reconnect within the same process. This matches prior behavior.

Link to Devin session: https://app.devin.ai/sessions/3ea6d041e22243cda500f9884cc251e1
Requested by: @ashleeradka

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[devin-ai-integration]

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